Battle of Dangyin

The Battle of Dangyin was fought on 9 September 304 AD between the armies of Sima Ying and Sima Yue during the War of the Eight Princes. Sima Ying's vcitory allowed for him to depose Emperor Sima Zhong's nephew Sima Tan and his Empress, and he briefly controlled Jin China.

Background
In 303 AD, the Prince of Chengdu Sima Ying and the Prince of Hejian Sima Yong formed an alliance against the regent Sima Ai, who had refused to assist Sima Ying against a rebellion. Sima Ying suggested to Sima Ai that they split the empire between them in exchange for Sima Ai executing his right-hand man Huangfu Shang, but Sima Ai refused, and Minister of Works Sima Yue captured Sima Ai and sent him to Sima Yong's general Zhang Fang, who had him burned to death. Sima Ying was now the new regent of Jin China, and he appointed Sima Yue President of State Secretariat. However, he sent his general Shi Chao with 50,000 troops to guard Luoyang, and, on 8 April 304 AD, he exerted his power by imprisoning the Empress and deposing Emperor Sima Zhong's nephew Sima Tan, making himself Crown Prince. Sima Yue rebelled Luoyang and restored the Empress and her nephew to their positions, and he amassed an army of 100,000 troops to march on Ying's capital.

Battle
Sima Ying's general Shi Chao, who had been guarding Luoyang, led his 50,000-strong army to meet Sima Yue's 100,000-strong army in battle. Shi Chao confronted Sima Yue and defeated him heavily at Dangyin, wounding and capturing the Emperor and forcing Sima Yue to flee back to his capital of Donghai in Shandong. Sima Yong, who was still allied to Sima Ying, then sent his army to occupy Luoyang, and Sima Tan and the Empress were once again deposed.

Aftermath
Sima Ying's victory, however, was short-lived. When Jia Nanfeng's loyal general Wang Pengzu rebelled against Sima Ying in the north, Sima Ying brought in the Xiongnu leader Liu Yuan to suppress the rebellion, but Liu Yuan instead founded the kingdom of Han Zhao in an attempt to restore the Han dynasty, whose emperors were partially descended from Xiongnu princesses. Liu Yuan's army soon swelled to 50,000 troops, and Sima Ying's 15,000-strong army deserted him while being ordered to escort the Emperor to Luoyang. Sima Yong's general Zhang Fang then took possession of the Emperor, moving him to Chang'an; Sima Yong then stripped Sima Ying from his position as heir and made Sima Zhi the crown prince.